In semiconductor lithography (or photolithography), the fabrication of an integrated circuit (IC) includes performing a variety of physical and chemical processes on a semiconductor (for example, silicon) substrate (which is also referred to as a wafer). A photolithography exposure apparatus or scanner is a machine that applies a desired pattern onto a target portion of the substrate. The wafer is irradiated by a light beam that extends along an axial direction, and the wafer is fixed to a stage so that the wafer generally extends along a plane that is lateral (and orthogonal) to the axial direction. The light beam has a wavelength in the deep ultraviolet (DUV) range, for example, from about 10 nanometers (nm) to about 400 nm.
The light beam is produced by an optical source. An accurate knowledge of spectral features or properties (for example, bandwidth and wavelength) of the light beam can be used, for example, to enable control of a minimum feature size or critical dimension (CD) at the wafer. The CD is related to the feature size that is printed on the wafer.